1. Field of the Invention
The invention relates to a process of producing electrical devices and more particularly to a process of producing charge coupled devices for sensors and memories.
2. Prior Art
Charged coupled devices (sometimes referred to as CCD-arrangements or CCD-devices) for sensors and memory are known. For example, W. S. Boyle et al in Bell Syst. Techn. J., pages 587-593 (April 1970) disclose a CCD device of this type which generally consist of a semiconductor body having an electrically insulating layer applied thereon, with metal electrodes. Such metal electrodes are separated from one another by spacings. The operative principle of such CCDs is to store minority charge carriers by connecting a voltage to a metal electrode on the surface of the semiconductor and to shift these minority charge carriers from one electrode to the next electrode by connecting appropriate voltages. Arrangements of this type are useful in constructing particularly good shift registers.
M. Kleefstra, "First Experimental Bi-Polar Charge-Coupled Devices", Microelectronics, Vol. 7, No. 2, pages 68-69, (1975), Mackintosh Publications Ltd., Luton, suggests a CDD wherein a n-silicon trough containing a shift channel of the CCD is arranged in a p-silicon substrate. Such trough contains p-doped zones which are separate from one another, with a control electrode arranged in each case above a gap between two p-doped zones and above portions of the p-doped zones adjoin such gap. An.sup.+ -doped region is provided in the n-silicon trough at each end of the shift channel, which is composed of the p-doped zones. By connecting a positive potential, which is sufficiently high relative to the p-doped zones, to the n-doped regions, it is possible to reduce the charge carriers in that part of the n-silicon trough located between the p-doped zones. This arrangement electrically connects the control electrodes and the p-silicon substrate. At this juncture, the channel no longer contains any moving charge carriers. The positive space charge in the channel is compensated by the negative space charge in the p-doped zones. Assuming that no noticeable vertical or lateral current is flowing between the p-doped zones and that no breakthrough voltage occurs, it is possible to change the channel potential by varying the potential across the control electrodes. By connecting modulating pulses to the control electrodes it is possible to sufficiently reduce the potential between adjacent control electrodes so as to enable charge transport to take place. With a homogeneous doping of the n-silicon trough, potential walls which weaken the charge transport can be formed between the control electrodes.